(1) Field of the Invention
The present invention relates to a butene-1 copolymer composition, and in particular, to a butene-1 copolymer composition which has excellent heat sealing properties, mechanical characteristics, moldability, and transparency without lowering its surface characteristics.
(2) Description of the Related Art
In recent years, butene-1 copolymer has come to notice as a soft or semi-soft resin.
However, since butene-1 copolymer has a maximum melting point (DSC measurement) of 120.degree. C., its heat sealing temperature is too high for it to be molded into a film, and it has problems such as practical use.
Therefore, a method is proposed for lowering the heat sealing temperature of the butene-1 copolymer (cf. Japanese Patent Application Laid-Open No. 108615/86, and Japanese Patent Application Laid-Open No. 38414/85). However, in order to lower the heat sealing temperature to a temperature that is sufficiently low for practical use, a considerably large amount of another .alpha.-olefine must be copolymerized. As a result, the film is likely to stick and block, thereby lowering the other properties the film must be provided with in order to make it suitable for practical use.
A composition is also known in which a large amount of propylene copolymer is mixed with butene-1 copolymer. (cf. Japanese Patent Application Laid-Open No. 108647/86 and Japanese Patent Application Laid-Open No. 118449/86 [U.S. Pat. No. 655397]).
However, the copolymers described in these official publications had the problem that the heat sealing temperature does not lower to sufficiently practical level, because so much propylene copolymer is mixed as to make the melting point of the propylene copolymer dominant.